Biological sample desalting and buffer replacement based on electromigration in a discontinuous electrolyte system...

The quality and yield of DNA specimens are essential for downstream analyses. Complex biological or environmental samples contain interfering compounds requiring advanced protocols for removing salts, small organic molecules, and/or proteins without compromising the DNA fragments distribution in the original sample. High-molecular-weight DNA fragments are often discriminated by standard extraction methods in attempts to remove the highly concentrated inorganic sample components.

Here, we introduce a simple device for the simplification, purification, desalting, and buffer exchange of complex biological samples based on electrodialysis in discontinuous electrolyte systems. The device combines a 3D-printed body with two electrolyte reservoirs and commercially available cassettes with dialysis membranes as inserts. Upon applying an electric current via electrodes inside the electrolyte reservoirs, the sample ions, injected into the cassette or one of the electrolyte reservoirs, electromigrate across the dialysis membranes. During this process, small sample ions pass through the membrane and are substituted by the ions of the selected buffers loaded into the electrolyte reservoirs. The larger ions, such as DNA fragments or proteins, stay in the sample reservoir. The performance of the device was evaluated using DNA samples in blood plasma. Several milliliters of a plasma sample were purified in 30 min with 90 % DNA recovery.

The device enables fast and effective purification of highly complicated samples. It can be easily scaled for the available sample amount (ranging from microliters to milliliters) and the analyte size of interest by selecting appropriate membrane pore sizes. The device's applicability was optimized on DNA samples with high salt content and tested on plasma samples. But it also has the potential for purification/desalting of a wide range of biological compounds, including proteins, peptides, or charged oligosaccharides, as well as organelles, cells, viruses, or bacteria.